A time analysis of a reference minutiae-based fingerprint matching system is presented. We study the relation between the score generated by the system (NFIS2 from NIST) and the time required to produce the matching score. Experimental results are carried out on a subcorpus of the MCYT database and show a clear correlation between both matching variables (time and score). Thus, a new threat against biometric systems is arisen as attacks based on the matching score could be largely simplified if the time information is used instead.